The present invention relates to an ink jet printing method and apparatus for effecting image formation on a print medium using ink.
In an ink jet printing apparatus, ink droplets ejected from a printing head carried on a printing apparatus are deposited on a print medium, and the ink is fixed and colored on the print medium, thus providing a print of the image. A color image printing is possible when a plurality of color inks, such as cyan, magenta, yellow and black inks are used. In an usual ink jet printing apparatus, a printing head is provided with a plurality of ejection outlet arrays corresponding to the respective colors of the ink. From the ejection outlet arrays, respective colors of inks are detected to provide a color image print.
In order to prevent bleeding of the image formed on the print medium, the ink having a relatively high perviousness relative to the print medium such as paper is often used for the color or chromatic ink. On the other hand, as for the black ink which is frequently used to form letter images, the ink having a relatively low perviousness is often used to provide clear ages of the letter images. This is because when the black ink having a high perviousness is deposited on the paper, the ink penetrates relatively quickly along the fibers of the paper, and therefore, the edges of the letter image may be non-smooth.
In such an ink jet printing apparatus using the black ink having the relatively low perviousness and the color ink having the relatively high perviousness, there is a liability of a problem that when the black ink and the color ink are contacted to each other on the print medium, the ink bleeding occurs at the boundary between the black ink and the color ink (this problem will hereinafter be called xe2x80x9cblack-color bleedingxe2x80x9d.
FIG. 1 shows an example of ejection outlet array arrangement in a printing head which is designed for avoiding such a problem. The printing head PH shown in this Figure comprises an ejection outlet array Bkl for ejecting the black ink (Bk), and a plurality of ejection outlet arrays for ejected the cyan (C), the magenta (M) and the yellow (Y), respectively. The shown arrangement of the ejection outlet arrays is applicable to a printing head which completes printing on the print medium by repetition of the recording operation with reciprocal scanning in the main scan direction of the printing head and recognition of feeding the print medium (paper feeding operation), that is, a so-called serial type recording device. In the Figure, an arrow M indicates the main scan direction. In the case of bidirectional print in which the ink is ejected in both of the forward and backward movements of the print head, two arrays of each of cyan, magenta and yellow ejection outlets are provided symmetrically with respect to the print scanning direction, as indicated by reference characters C1, C2, M1, M2, Y1, Y2, in order to provide the same ejection orders of the color inks respective of the directions of the scanning.
When only a black image is to be printed, all of the ejection outlets for the black ink are used, but when a color image is to be printed, only the portion, indicated by xe2x80x9caxe2x80x9d of the black ejection outlets is used, and as for the color ejection outlets, the portion indicated by xe2x80x9cbxe2x80x9d is used.
With this structure, the black image data are printed on the print medium by the scanning of the printing head in the horizontal direction (main-scanning) in the Figure, using only the ejection outlet array a, and thereafter, the print medium is fed through a distance an in the vertical direction (sub-scan, or paper feeding). In the next main-scanning of the printing head, the printing is effected by the color ejection outlet arrays b, by which the image printing is completed for 1 print region. When the color ejection outlet array b carries out the printing, the black ejection outlet array portion a prints the black part of the image for the next print region.
According to this method, the color ink is ejected onto the print medium in the print scanning subsequent to the scanning of ejecting the black ink onto the print medium. Therefore, as compared with the case in which the black ink and the color ink are simultaneously ejected onto the same print region in one print scanning, there is a time period in which the black ink penetrates into the print medium and fixes, prior to the ejection of the color ink. Therefore, this method is advantageous from the stern point of suppressing the occurrence of the black-color bleeding.
However, when the bi-directional print is effected using such a printing head, the black image is printed in the forward scanning, and then, the color ink image is printed in the subsequent backward scanning, for example. In this case, after the printing of the last part of the black image in the forward scanning, the color ink image printing after the paper feeding starts with this part (the final portion of the black image formation in the previous print scanning). For this reason, at either one of the left and right edges of the completed print, the time period from the printing of the black ink onto the print medium and the printing of the color ink thereonto (black-color time difference) is relatively short, and it is relatively long at the other edge. Where the black-color time difference is a small, the black-color bleeding tends to occur. In addition, the lower end of the color ink ejection ejection outlet array b and the upper end of the black ink ejection outlet array portion a (portion c in the Figure) are adjacent to each other in the sub-scan direction (paper feeding direction), and therefore, the color ink and the black ink having the different perviousness and the like are contacted to each other with the result of bleeding occurrence. Additionally, surfactant contained in the color ink, for example, might flow into the black ink with the result of lowering of the interface tension of the black ink, which leads to movement of the black ink. If this occurs, the image density at this portion decreases, does deteriorating the image quality.
FIG. 2 shows another example of arrangement of the ejection outlet array in which a spacing corresponding to the distance of one sheet feeding operation between the black ejection outlet array and the color ejection outlet array when the color images are formed. In this Figure, as for the black ejection outlet array, only the portion used for the color image formation is shown.
With this structure, the black ink is ejected onto the print medium from the black ejection outlet array in a forward scanning, for example. Then, the paper feeding is carried out, but in the subsequent backward scanning of printing, the ink is not ejected onto this position on the print medium. The paper feeding is further carried out, and in the next forward scanning, the color ink is printed onto this position, thus completing the printing of one printing region. In this system, there is a time difference corresponding to one print scanning from the black ink shot to the color ink shot. This is advantageous over the arrangement shown in FIG. 1 from the standpoint of preventing the black-color bleeding. It is considered that at the left and right positions on the print medium, the black-color time differences are equal in one print region, and therefore, this arrangement is advantageous from the standpoint of preventing the deterioration of the image quality.
However, the inventors investigations have revealed a problem with the arrangement shown in FIG. 2, depending on the control of the recording operation.
For example, the black ink is printed on the print medium in the forward scanning, and thereafter, the sheet is fed, and then, the backward print scanning is carried out. To the region on the print medium to which the black ink has just been printed, the color ink is not printed, as described hereinbefore. However, if the color ejection outlet array prints the color ink to form image in another (adjacent) region on the print medium during the backward printing scanning operation, there is a possibility that color ink is shot to the area close to the area to which the black ink has been shot. At either one of left and right ends, the color ink is shot with a short time difference from the shot of the black ink, closely to the black ink shot area. Then, the deterioration of the image quality because of the above-described black-color bleeding and difference in the perviousness between the black ink and color ink, results.
The arrangement of the ejection outlet array shown in FIG. 3, is an example in which the distance between the black ejection outlet array and the color ejection outlet array is slightly larger than the distance of the one paper feeding, as a countermeasure against the problem. According to the arrangement shown in FIG. 3, the problem with the arrangement of FIG. 2 can be avoided.
The printing operation with the arrangement FIG. 3 will be described. The relative to positional relationship between the image formed on the print medium by the black ejection outlet array and the printing head is shown in (1), and then, the sheet is fed, by which the positional relationship is as indicated by (2). With disposition of relationship, the subsequent print scanning operation is carried out. As will be understood from the Figure, even if the color ejection outlet arrays eject the ink on the print medium, the ink is not overlaid or is not close to the position of the image previously printed.
When the sheet is further fed, the positional relationship becomes as shown in (3), which is the position where the first black ink is printed. In the subsequent print scanning apparatus, the color ink is ejected for a hatched region d. The sheet is further fed, and the relative to position becomes as indicated by (4), which is the position of the first black ink printing. Then, the color ink is ejected to the hatched region e, by which the image printing is completed for the one printing area.
However, it has been found that with this arrangement, there still remains a problem. As for the region d on the print medium, the black ink is ejected, and then one scanning operation is carried out without ejection of the ink, and then the color ink is ejected. On the other hand, as of the region e in the Figure, the black ink is ejected, and the color ink is ejected after two scanning operations without ejection of the ink. Therefore, the same period from the ejection of the black ink onto the print medium to the ejection of the color ink is not uniform, and this would result in band-like non-uniformity appearing in the image. The problems arising in the recording operations with the arrangements for FIGS. 2, 3 are small decrease of the image quality. However, in the case of the recording device with which a high image quality is desired, the problem is to be solved.
As a modification of the arrangement of FIG. 3, it would be considered that distance between the black ejection outlet array and the color ejection outlet array is extended to that corresponding to two printing scans or more. However, if this is done, the size of the printing head becomes bulky, and the cost of the printing head rises. Additionally, it becomes difficult to provide a uniform fine gap between the printing head and the print medium.
The inventors have confirmed through experiments that deteriorations of the image quality attributable to the difference in the pervious between the black ink and the color ink and to the black-color bleeding, tended to occur where a relatively large amount of black ink is printed onto the print medium, and the ink dots are continuous on the print medium. The deteriorations of the image quality attributable to the difference in the fixing state and the penetration of the ink due to the difference, depending on the areas on the print medium, in the time difference from the shot of the black ink to the shot of the color ink, tend to occur where a relatively small amount of black ink is ejected onto the print medium, and the black ink dots are not yet continuous. It has also be found that phenomena are significantly influenced by the amount of the color ink.
Accordingly, it is a principal object of the present invention to provide a solution to at least one of the above-described problems, wherein proper print controlling modes are selected depending on the image data to be printed.
According to an aspect of the present invention, there is provided an ink jet printing apparatus comprising print means having a polarity of ejection outlet arrays each having a plurality of ejection outlets, arranged in a predetermined direction, for ejecting ink, scanning means for scanningly moving said print means relative to the print medium in a main scan direction which is different from the predetermined direction during a printing operation, and means for feeding the print medium relative to said print means in a direction which is different from the main scan direction, wherein an image is formed on the print medium while repeating scanning operation of said scanning means and feeding operation by said feeding means, comprising: information obtain means for obtaining image information corresponding to at least one of said ejection outlet arrays with respect to a predetermined area of image data to be printed; and selecting means for selecting such a portion in said at least one of ejection outlet arrays as is to effect printing for the image data in the predetermined area, on the basis of the information obtained by said information obtaining means upon image formations.
According to another aspect of the present invention, there is provided an ink jet printing method comprising a step of preparing print means having a polarity of ejection outlet arrays each having a plurality of ejection outlets, arranged in a predetermined direction, for ejecting ink, a step of scanningly moving said print means relative to the print medium in a main scan direction which is different from the predetermined direction during a printing operation, and a step of feeding the print medium relative to said print means in a direction which is different from the main scan direction, wherein an image is formed on the print medium while repeating scanning operation of said scanning step and feeding operation of said feeding step, comprising an information obtaining step of obtaining image information corresponding to at least one of said ejection outlet arrays with respect to a predetermined area of image data to be printed; and a selecting step of selecting such a portion in said at least one of ejection outlet arrays as is to effect printing for the image data in the predetermined area, on the basis of the information obtained by said information obtaining step upon image formations; and a step of forming an image with a portion in the ejection outlet array selected by said selection step.
According to the present invention, there is provided a printing apparatus wherein an image is formed on a print medium using at least two ejection outlet arrays which are disposed with deviation in the print medium feeding direction and in the scanning direction which is perpendicular to the feeding direction, said apparatus comprising means enabling image formations using a plurality of portions in one ejection outlet array for image data of a predetermined area, wherein the print data assigned to the plurality of portions are changed on the basis of the image data of the predetermined area containing the image data. In other words, the image data is checked for each of predetermined areas, and the advantageous print control more being selected so that expected deterioration of the image quality is avoided.
These and other objects, features and advantages of the present invention will become more apparent upon a consideration of the following description of the preferred embodiments of the present invention taken in conjunction with the accompanying drawings.